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Long-term toxicity to aquatic invertebrates

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Description of key information

21 d NOEC ≥15 µg/l based on growth and reproduction, Daphnia magna, measured (Springborn Laboratories 1990e, Smithers Viscient 2018)

21 d EC50 >15 µg/l based on survival and reproduction, Daphnia magna, measured (Springborn Laboratories 1990e)

Key value for chemical safety assessment

Additional information

A 21-day NOEC of 7.9 µg/l had been determined for the effects of the test substance on survival and reproduction of Daphnia magna. A 21-day EC50 of >15 µg/l has also been determined in the same test for effects on mortality (Springborn Laboratories 1990e). Re-evaluation of this study indicates that based on the classic chronic daphnid endpoints of reproduction and growth, the 21-day NOEC of D4 was determined to be 15 µg/l (Smithers Viscient, 2018). There has also been discussion regarding the validity of the initially reported NOEC value for survival of 7.9 μg/L. The overall survival rate of 77% in the high dose group is the arithmetic mean of just 2 replicates, where in fact only in 1 replicate was there a survival rate below 80% (replicate 1: 67%; replicate 2: 87%). Also, Fairbrother and Woodburn (2016) report that the effect concentration on Daphnia survival (77%) was only slightly below the allowable 80% survival rate for controls. In this study, no adverse effects on reproduction or growth were observed. The reproduction and growth of neonates is the population-relevant endpoint and should take precedence in the scientific evaluation of the study and assignment of a NOEC.  Although the mortality 21-d NOEC had been determined as 7.9 µg/l, there is a lot of uncertainty associated with this NOEC due to differences in the two replicates and the fact that the overall survival rate of 77% is only slightly below the allowable rate. Above that, the reproduction and growth of neonates is the population-relevant endpoint. Therefore the 21-d NOEC for growth and reproduction of ≥15 µg/L was taken as a key value for the chronic invertebrate toxicity endpoint.